1. Field of the Invention
The present invention relates a cleaning method of semiconductor manufacturing apparatus and semiconductor manufacturing apparatus such as film forming apparatus.
2. Description of the Related Art
Film forming apparatuses such as low pressure CVD (chemical vapor deposition) apparatuses are typically used for forming films on semiconductor substrates in the manufacturing process of semiconductors.
FIG. 1 shows a schematic cross sectional view of a low pressure CVD apparatus. According to FIG. 4, the apparatus comprises a reaction tube 103 including an inner tube 103a and an outer tube 103b where a boat 102 carrying a plurality of semiconductor substrates 101 to be processed is mounted and a closure 104 for sealing the reaction tube. The reaction tube 103 is connected to a reaction gas feed pipe 105, which is included in a supply system, also connected to a vacuum pump 106, which is included in an exhaust system, through a gate valve 107. A heater 108 is arranged around the reaction tube to heat reaction gas.
Part of excessive gas not participating in the film forming accumulates as reaction byproducts 109 near the closure 104 at an end of the reaction tube 103. As the film forming process is repeated, the amount of the adhering and accumulating reaction byproducts 109 increases. Then, part of the reaction byproducts 109 come off, to float in air and contaminate the semiconductor substrates to be processed so that they usually removed by cleaning gas. However, it has been difficult to effectively remove floating small-particles (foreign-material) 110 that are not moved away on the exhaust gas flow.
Meanwhile, as a method for cleaning small-particles in an etching apparatus, it is suggested that introducing steam under reduced pressure using the small-particles as cores for solidification/liquefaction to make small-particles removable (see, for example, Jpn. Pat. Publication No. 11-54485). However, it has been difficult to apply any of the method to the film forming apparatus, because an injection channel has to be additionally provided to inject a foreign object such as steam into the film forming apparatus, and a tiny amount of the injected foreign object is remaining in the apparatus, it can adversely affect the film forming process and contaminate the semiconductor substrates to be processed.